In power IC applications, an interface generally serves to manage functions such as power level, or on and off switching. In the load switch power IC case, the IC either delivers power to a subsystem or not depending on the state of the on/off pin. In a more complex power supply controller, the regulated output voltage is set by a more complex interface such as an integrated 5-pin digital to analog interface. When many subsystems exist within the same system, an even more complex interface, such as the SMBUS interface may be implemented.
The complex power IC can easily afford a multi-pin control interface, since it is already in a large package, and has sufficient functional density. The stand-alone power management function cannot normally offer a complex control interface due to die size or package size constraints. Still there are cases where this type of control is desirable. For instance, it may be desirable to vary a current limit over different load scenarios. However, few pins are available for control of the simple load switch because most of the pins are used by the power function, and there is no board space or budget for a larger package. Some functionality can be added by means of an analog interface, but since most applications are controlled by a microprocessor, a digital interface is easiest to implement and most cost effective. A serial interface is efficient, but common simple serial interfaces such as 3-wire or 2-wire require too many pins. Complex serial interfaces such as SMBUS are generally too complex and expensive to merit implementation for the stand-alone power management function.
For these reasons and others, there is a need for an interface that may be used to control stand-alone power and other IC types. Ideally, this interface would be able to accommodate a wide variety of control needs and be scaleable to many levels of complexity. Minimal pin use is also desirable, with the ideal being use of a single pin that may optionally be shared with another function.